In many applications, the operating times of spark ignition, internal combustion engines need to be accurately monitored. For example, engines used in military inflatable crafts which are stored underwater for covert operations must be strictly maintained every dozen hours. Aircraft engines, whether military or civilian, must also be strictly maintained according to actual operating hours. Rental vehicles, boats, generators, construction equipment, or anything powered by spark ignition engines that are rented hourly all require accurate and reliable accounting of the machines' operating times.
Engine operating time logs, or meters, for monitoring total engine operating time have been available for many years. On older spark ignition engines in which the sparks are generated from a low voltage source such as a battery, the monitoring device is usually an electro-mechanical hour counter (Hobbs meter) powered by the vehicle's battery. The counter is triggered by the engagement of the ignition system. When the ignition system is turned on, the counter will begin its timing operation; when the ignition is turned off, the counter will cease its timing operation. The elapsed time thus indicates the ignition system's operating time. The elapsed times of each operation are added together to produce the accumulated or total operating time of the engine. Another common type of hour log determines engine operating time by counting the number of spark impulses at a predetermined engine speed. These devices have many drawbacks:
A. Many must be specifically configured, by the user, for the number of cylinders in the engine to be monitored. An improperly configured unit will produce erroneous readings. Because many users do not read instructions, improper configuration often occurs. PA1 B. They require at least a three wire hookup: One wire for attaching to the ignition system, and two for attaching to the vehicle's battery. Because long wires must be routed to several distant locations, they must be laboriously secured along their lengths. Otherwise, they could become tangled in the moving parts of the engine. PA1 C. Because they rely on the vehicle's battery for power, those which use electronic timers will loose their data when the vehicle's battery is disconnected, such as during battery replacement, or during regular engine servicing. PA1 D. Many of these devices monitor the operating time of the engine's ignition system, not the actual running time of the engine itself. Therefore, if the ignition system is turned on without the engine running, they will produce erroneous readings. PA1 E. Those devices which count spark impulses will produce erroneous readings if the engine is not operated constantly at the single, predetermined speed. PA1 F. The Hobbs meter cannot be used on modern, multi-cylinder engines which do not use a spark distributor, but generate spark voltages for each cylinder individually. PA1 G. Many of these device have main housings which must be mounted away from the heat and fuel lines of the engine. This will require very long hookup wires, and complicates installation.
Currently, Autonnic Research International, Inc. in Hayward, Calif., produces a compact engine time log which monitors accumulated engine operating time for spark ignition engines, which hereinafter will be known as the reference device. It is self-contained in a single case, which has an integral metal mounting/grounding tab extending from it for mounting the time log directly onto an electrically grounded engine block. The reference device is the first time log to be self-powered, which eliminates the need for cumbersome power hookup, and maintains the data even when unit is disconnected from the engine. It uses extremely low power CMOS (Complementary-Metal Oxide Semiconductor) components and an extremely long life lithium battery. An insulated lead wire with a capacitive sensor clip at the distal end, or flying sensor clip, extends from the device for attaching to a spark plug wire or ignition wire. Because the self-powered reference device is mounted directly onto the engine, the sensor lead can be very short. The reference device is heat resistant, and is tightly sealed against liquid intrusion and tampering. These features make installation very easy.
The reference device, which senses spark impulses in the ignition wire, will begin counting when pulses begin passing through the ignition wire, and will stop counting when the pulses cease. The elapsed time during which sparks are present represent the engine operating time. The delayed start ensures that the engine is actually running before the timer is activated. A LCD (Liquid Crystal Display) panel on the device shows the total accumulated engine operating time, in tenths of an hour, to 19,999.9 hours. The reference device may be used on any type of spark ignition engine, regardless of the type of ignition system, the number of cylinders, the number of strokes, or engine speed. Therefore, it has no need for adjustments or setup. Because of the design and quality of its components, it has a known operating life which exceeds ten years, and a projected life of twenty years. It also has an accuracy of .+-.3 seconds per thousand hours of running time. These superior qualities has enabled the reference device to be adopted by the U. S. Navy. However, because it must be bolted directly onto an engine block, it will require the removal of a bolt from the engine. This will void a commercial engine's warranty.
The Running Time Meter.TM. made by Computime, Inc. of Denham Springs, La., was introduced after the reference device has become known. It is the only other self-powered time log on the market. However, it has a main housing which must be mounted some distance away from the heat and fuel lines of an engine, which will necessitate routing long lead wires through the engine compartment. Moreover, it has a sensing wire which must be wrapped many turns around an ignition wire, the number of turns being dependent upon the length of the sensing wire, and largely determined by trial-and-error. As a result, installation is cumbersome.
In conclusion, existing engine time logs are either cumbersome to install and setup, susceptible to producing incorrect readings, vulnerable to data loss, or will void the manufacturers' warranty of commercial engines.